1. Field of the Invention
The present invention relates to a rocker arm changeover device for an engine.
2. Description of the Related Art
A structure of related art for an internal combustion engine, such as a gasoline engine or a diesel engine (hereinafter, merely referred to as engine), changes valve-opening characteristics, such as an open/close timing, a lift amount, and a non-operation state, of at least one of an intake valve and an exhaust valve in accordance with an operating state in order to increase output and fuel consumption efficiency and to decrease noxious exhaust gas components. A mechanism that changes the valve-opening characteristics may be, for example, a structure including a high-lift cam and a low-lift cam classified depending on the lift amount of a valve; a plurality of rocker arms capable of making rocking motions by the cams; and changeover pins that change an engagement state of the rocker arms between engagement and disengagement (for example, see Japanese Patent No. 3396412).
Japanese Patent No. 3396412 includes a low-speed rocker arm serving as a major rocker arm that drives a valve, and medium-speed and high-speed rocker arms serving as driven rocker arms arranged on both sides of the low-speed rocker arm. The rocker arms can make rocking motions by cams respectively corresponding to the rocker arms. The medium-speed or high-speed rocker arm is engaged with or disengaged from the low-speed rocker arm by changeover pins. The changeover pin provided for the low-speed rocker arm arranged at the center is divided at a middle position in an axial direction with a gap interposed between the divided portions. The gap is provided to selectively allow one of the changeover pins provided in the rocker arms on both sides to protrude into the gap.
The structure disclosed in Japanese Patent No. 3396412 having the above-described changeover pin mechanism engages the low-speed rocker arm with the other rocker arms through the changeover pins that protrude from the other rocker arms and are inserted into the low-speed rocker arm. However, to prevent the pins from tilting, the changeover pins to be engaged have to have certain lengths. To allow the long changeover pins to protrude or be retracted, the rocker arms have to have large widths in the axial direction of the changeover pins. If the rocker arms with the large widths are arranged on both sides, the mechanism including the plurality of rocker arms arranged in line may become large.
Alternatively, an engagement state may be attained such that divided changeover pins provided in the low-speed rocker arm protrude and are inserted into the other rocker arms. In this case, the other rocker arms may have changeover pins that are only required to push back the divided changeover pins. Hence, the changeover pins may have small lengths. Thus, the mechanism can be small. However, with the structure disclosed in Japanese Patent No. 3396412, since the divided changeover pins have the small axial lengths, the pins may tilt while being engaged.